New optional ZONE arg for format-time-string etc.

This simplifies time conversions in other time zones.
It also prevents display-time-world tampering with TZ (Bug#21020).
* admin/admin.el (add-release-logs):
Use improved add-log-time-format API.
* admin/merge-gnulib (GNULIB_MODULES): Add time_rz, timegm.
(GNULIB_TOOL_FLAGS): Avoid flexmember, setenv, unsetenv.
* configure.ac (tzalloc): Remove test for this, since
Emacs no longer uses HAVE_TZALLOC directly.
* doc/lispref/os.texi (Time of Day, Time Conversion)
(Time Parsing):
* etc/NEWS: Document the new behavior.
Merge from gnulib, incorporating:
2015-07-25 strftime: fix newly-introduced bug on Solaris
2015-07-23 fprintftime, strftime: use timezone_t args
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* lib/strftime.c, lib/strftime.h, lib/time.in.h, m4/sys_time_h.m4:
* m4/time_h.m4:
Update from gnulib.
* lib/time_rz.c, lib/timegm.c, m4/time_rz.m4, m4/timegm.m4:
New files from gnulib.
* lisp/time-stamp.el (time-stamp-string):
* lisp/time.el (display-time-world-list)
(display-time-world-display):
Use new API, with time zone arg.
* lisp/time.el (display-time-world-display):
Fix race when current-time advances while we're running.
* lisp/vc/add-log.el (add-log-iso8601-time-zone)
(add-log-iso8601-time-string): Accept optional time zone arg.
* lisp/vc/add-log.el (add-change-log-entry):
* lisp/vc/log-edit.el (log-edit-changelog-ours-p): Use new arg.
* nt/gnulib.mk: Propagate lib/gnulib.mk changes here.
Add rules for the time module, since they're now needed
for tzalloc etc.
* src/conf_post.h (getenv_TZ, setenv_TZ): New macros.
(emacs_getenv_TZ, emacs_setenv_TZ): New decls.
* src/editfns.c: Include errno.h.
(set_time_zone_rule): Omit unnecessary forward decl.
(initial_tz): Remove, replacing with ...
(local_tz, wall_clock_tz, utc_tz): New static vars and constants.
(tzeqlen): New constant; prefer it to (sizeof "TZ=" - 1).
(emacs_localtime_rz, emacs_mktime_z, xtzalloc, xtzfree)
(tzlookup): New static functions.
(init_editfns): New arg DUMPING.  All uses changed.
(init_editfns): Omit most initialization if dumping, not if
!initialized.  Initialize wall_clock_tz and local_tz.
(emacs_nmemftime, format_time_string): Time zone argument can now
be any time zone, not just a boolean for UTC or local time.  All
callers changed.
(Fformat_time_string, Fencode_time, Fcurrent_time_string)
(Fcurrent_time_zone): New optional arg ZONE.
(Fdecode_time, Fset_time_zone_rule): ZONE arg can now also take
the same form as with the other new additions.
(decode_time_zone): Remove; no longer needed.
(tzvalbuf): Now file-scope.
(emacs_getenv_TZ, emacs_setenv_TZ): New functions.
(syms_of_editfns): Define Qwall.
* src/editfns.c (mktime_z) [!HAVE_TZALLOC]:
* src/systime.h (mktime_z, timezone_t, tzalloc, tzfree)
[!HAVE_TZALLOC]:
Remove; now supplied by gnulib.
* src/emacs.c (main):
* src/lisp.h (init_editfns): Adjust to init_editfns API change.

6 files changed, 483 insertions, 61 deletions

diff --git a/lib/gnulib.mk b/lib/gnulib.mk
index 2dd0ef82c3..1ca12a28be 100644
--- a/lib/gnulib.mk
+++ b/lib/gnulib.mk
@@ -21,7 +21,7 @@
 # the same distribution terms as the rest of that program.
 #
 # Generated by gnulib-tool.
-# Reproduce by: gnulib-tool --import --dir=. --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=close --avoid=dup --avoid=fchdir --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=open --avoid=openat-die --avoid=opendir --avoid=raise --avoid=save-cwd --avoid=select --avoid=sigprocmask --avoid=stdarg --avoid=stdbool --avoid=threadlib --makefile-name=gnulib.mk --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt binary-io byteswap c-ctype c-strcase careadlinkat close-stream count-one-bits count-trailing-zeros crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 dtoastr dtotimespec dup2 environ execinfo faccessat fcntl fcntl-h fdatasync fdopendir filemode fstatat fsync getloadavg getopt-gnu gettime gettimeofday gitlog-to-changelog intprops largefile lstat manywarnings memrchr mkostemp mktime pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat sig2str socklen stat-time stdalign stddef stdio stpcpy strftime strtoimax strtoumax symlink sys_stat sys_time time time_r timer-time timespec-add timespec-sub unsetenv update-copyright utimens vla warnings
+# Reproduce by: gnulib-tool --import --dir=. --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=close --avoid=dup --avoid=fchdir --avoid=flexmember --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=open --avoid=openat-die --avoid=opendir --avoid=raise --avoid=save-cwd --avoid=select --avoid=setenv --avoid=sigprocmask --avoid=stdarg --avoid=stdbool --avoid=threadlib --avoid=unsetenv --makefile-name=gnulib.mk --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt binary-io byteswap c-ctype c-strcase careadlinkat close-stream count-one-bits count-trailing-zeros crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 dtoastr dtotimespec dup2 environ execinfo faccessat fcntl fcntl-h fdatasync fdopendir filemode fstatat fsync getloadavg getopt-gnu gettime gettimeofday gitlog-to-changelog intprops largefile lstat manywarnings memrchr mkostemp mktime pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat sig2str socklen stat-time stdalign stddef stdio stpcpy strftime strtoimax strtoumax symlink sys_stat sys_time time time_r time_rz timegm timer-time timespec-add timespec-sub unsetenv update-copyright utimens vla warnings
 
 
 MOSTLYCLEANFILES += core *.stackdump
@@ -655,6 +655,17 @@ EXTRA_libgnu_a_SOURCES += mktime.c
 
 ## end   gnulib module mktime
 
+## begin gnulib module mktime-internal
+
+if gl_GNULIB_ENABLED_5264294aa0a5557541b53c8c741f7f31
+
+endif
+EXTRA_DIST += mktime-internal.h mktime.c
+
+EXTRA_libgnu_a_SOURCES += mktime.c
+
+## end   gnulib module mktime-internal
+
 ## begin gnulib module openat-h
 
 if gl_GNULIB_ENABLED_03e0aaad4cb89ca757653bd367a6ccb7
@@ -1589,10 +1600,12 @@ time.h: time.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H) $(
 	      -e 's/@''GNULIB_STRPTIME''@/$(GNULIB_STRPTIME)/g' \
 	      -e 's/@''GNULIB_TIMEGM''@/$(GNULIB_TIMEGM)/g' \
 	      -e 's/@''GNULIB_TIME_R''@/$(GNULIB_TIME_R)/g' \
+	      -e 's/@''GNULIB_TIME_RZ''@/$(GNULIB_TIME_RZ)/g' \
 	      -e 's|@''HAVE_DECL_LOCALTIME_R''@|$(HAVE_DECL_LOCALTIME_R)|g' \
 	      -e 's|@''HAVE_NANOSLEEP''@|$(HAVE_NANOSLEEP)|g' \
 	      -e 's|@''HAVE_STRPTIME''@|$(HAVE_STRPTIME)|g' \
 	      -e 's|@''HAVE_TIMEGM''@|$(HAVE_TIMEGM)|g' \
+	      -e 's|@''HAVE_TIMEZONE_T''@|$(HAVE_TIMEZONE_T)|g' \
 	      -e 's|@''REPLACE_GMTIME''@|$(REPLACE_GMTIME)|g' \
 	      -e 's|@''REPLACE_LOCALTIME''@|$(REPLACE_LOCALTIME)|g' \
 	      -e 's|@''REPLACE_LOCALTIME_R''@|$(REPLACE_LOCALTIME_R)|g' \
@@ -1624,6 +1637,24 @@ EXTRA_libgnu_a_SOURCES += time_r.c
 
 ## end   gnulib module time_r
 
+## begin gnulib module time_rz
+
+
+EXTRA_DIST += time_rz.c
+
+EXTRA_libgnu_a_SOURCES += time_rz.c
+
+## end   gnulib module time_rz
+
+## begin gnulib module timegm
+
+
+EXTRA_DIST += mktime-internal.h timegm.c
+
+EXTRA_libgnu_a_SOURCES += timegm.c
+
+## end   gnulib module timegm
+
 ## begin gnulib module timespec
 
 libgnu_a_SOURCES += timespec.c
@@ -1806,15 +1837,6 @@ EXTRA_DIST += unistd.in.h
 
 ## end   gnulib module unistd
 
-## begin gnulib module unsetenv
-
-
-EXTRA_DIST += unsetenv.c
-
-EXTRA_libgnu_a_SOURCES += unsetenv.c
-
-## end   gnulib module unsetenv
-
 ## begin gnulib module update-copyright
 
 
diff --git a/lib/strftime.c b/lib/strftime.c
index 2426aae705..c7cec2621c 100644
--- a/lib/strftime.c
+++ b/lib/strftime.c
@@ -121,22 +121,11 @@ extern char *tzname[];
 
 
 #ifdef _LIBC
+# define mktime_z(tz, tm) mktime (tm)
 # define tzname __tzname
 # define tzset __tzset
 #endif
 
-#if !HAVE_TM_GMTOFF
-/* Portable standalone applications should supply a "time.h" that
-   declares a POSIX-compliant localtime_r, for the benefit of older
-   implementations that lack localtime_r or have a nonstandard one.
-   See the gnulib time_r module for one way to implement this.  */
-# undef __gmtime_r
-# undef __localtime_r
-# define __gmtime_r gmtime_r
-# define __localtime_r localtime_r
-#endif
-
-
 #ifndef FPRINTFTIME
 # define FPRINTFTIME 0
 #endif
@@ -385,12 +374,7 @@ iso_week_days (int yday, int wday)
 
 /* When compiling this file, GNU applications can #define my_strftime
    to a symbol (typically nstrftime) to get an extended strftime with
-   extra arguments UT and NS.  Emacs is a special case for now, but
-   this Emacs-specific code can be removed once Emacs's config.h
-   defines my_strftime.  */
-#if defined emacs && !defined my_strftime
-# define my_strftime nstrftime
-#endif
+   extra arguments TZ and NS.  */
 
 #if FPRINTFTIME
 # undef my_strftime
@@ -398,8 +382,9 @@ iso_week_days (int yday, int wday)
 #endif
 
 #ifdef my_strftime
-# define extra_args , ut, ns
-# define extra_args_spec , int ut, int ns
+# undef HAVE_TZSET
+# define extra_args , tz, ns
+# define extra_args_spec , timezone_t tz, int ns
 #else
 # if defined COMPILE_WIDE
 #  define my_strftime wcsftime
@@ -411,7 +396,7 @@ iso_week_days (int yday, int wday)
 # define extra_args
 # define extra_args_spec
 /* We don't have this information in general.  */
-# define ut 0
+# define tz 1
 # define ns 0
 #endif
 
@@ -483,7 +468,7 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
   zone = (const char *) tp->tm_zone;
 #endif
 #if HAVE_TZNAME
-  if (ut)
+  if (!tz)
     {
       if (! (zone && *zone))
         zone = "GMT";
@@ -496,7 +481,12 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
       tzset ();
 # endif
     }
+  /* The tzset() call might have changed the value.  */
+  if (!(zone && *zone) && tp->tm_isdst >= 0)
+    zone = tzname[tp->tm_isdst != 0];
 #endif
+  if (! zone)
+    zone = "";
 
   if (hour12 > 12)
     hour12 -= 12;
@@ -1144,7 +1134,7 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
             time_t t;
 
             ltm = *tp;
-            t = mktime (&ltm);
+            t = mktime_z (tz, &ltm);
 
             /* Generate string value for T using time_t arithmetic;
                this works even if sizeof (long) < sizeof (time_t).  */
@@ -1319,14 +1309,6 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
               to_lowcase = true;
             }
 
-#if HAVE_TZNAME
-          /* The tzset() call might have changed the value.  */
-          if (!(zone && *zone) && tp->tm_isdst >= 0)
-            zone = tzname[tp->tm_isdst != 0];
-#endif
-          if (! zone)
-            zone = "";
-
 #ifdef COMPILE_WIDE
           {
             /* The zone string is always given in multibyte form.  We have
@@ -1366,7 +1348,7 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
 #if HAVE_TM_GMTOFF
             diff = tp->tm_gmtoff;
 #else
-            if (ut)
+            if (!tz)
               diff = 0;
             else
               {
@@ -1375,7 +1357,7 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
                 time_t lt;
 
                 ltm = *tp;
-                lt = mktime (&ltm);
+                lt = mktime_z (tz, &ltm);
 
                 if (lt == (time_t) -1)
                   {
@@ -1384,7 +1366,7 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
                        occurred.  */
                     struct tm tm;
 
-                    if (! __localtime_r (&lt, &tm)
+                    if (! localtime_rz (tz, &lt, &tm)
                         || ((ltm.tm_sec ^ tm.tm_sec)
                             | (ltm.tm_min ^ tm.tm_min)
                             | (ltm.tm_hour ^ tm.tm_hour)
@@ -1394,7 +1376,7 @@ strftime_case_ (bool upcase, STREAM_OR_CHAR_T *s,
                       break;
                   }
 
-                if (! __gmtime_r (&lt, &gtm))
+                if (! localtime_rz (0, &lt, &gtm))
                   break;
 
                 diff = tm_diff (&ltm, &gtm);
@@ -1473,15 +1455,3 @@ my_strftime (STREAM_OR_CHAR_T *s, STRFTIME_ARG (size_t maxsize)
 #if defined _LIBC && ! FPRINTFTIME
 libc_hidden_def (my_strftime)
 #endif
-
-
-#if defined emacs && ! FPRINTFTIME
-/* For Emacs we have a separate interface which corresponds to the normal
-   strftime function plus the ut argument, but without the ns argument.  */
-size_t
-emacs_strftimeu (char *s, size_t maxsize, const char *format,
-                 const struct tm *tp, int ut)
-{
-  return my_strftime (s, maxsize, format, tp, ut, 0);
-}
-#endif
diff --git a/lib/strftime.h b/lib/strftime.h
index 3967afc494..2ce6cc5768 100644
--- a/lib/strftime.h
+++ b/lib/strftime.h
@@ -23,11 +23,10 @@ extern "C" {
 
 /* Just like strftime, but with two more arguments:
    POSIX requires that strftime use the local timezone information.
-   When __UTC is nonzero and tm->tm_zone is NULL or the empty string,
-   use UTC instead.  Use __NS as the number of nanoseconds in the
-   %N directive.  */
+   Use the timezone __TZ instead.  Use __NS as the number of
+   nanoseconds in the %N directive.  */
 size_t nstrftime (char *, size_t, char const *, struct tm const *,
-                  int __utc, int __ns);
+                  timezone_t __tz, int __ns);
 
 #ifdef __cplusplus
 }
diff --git a/lib/time.in.h b/lib/time.in.h
index 1a6b746cca..a983f498e5 100644
--- a/lib/time.in.h
+++ b/lib/time.in.h
@@ -231,6 +231,25 @@ _GL_CXXALIAS_SYS (strptime, char *, (char const *restrict __buf,
 _GL_CXXALIASWARN (strptime);
 # endif
 
+# if defined _GNU_SOURCE && @GNULIB_TIME_RZ@ && ! @HAVE_TIMEZONE_T@
+typedef struct tm_zone *timezone_t;
+_GL_FUNCDECL_SYS (tzalloc, timezone_t, (char const *__name));
+_GL_CXXALIAS_SYS (tzalloc, timezone_t, (char const *__name));
+_GL_FUNCDECL_SYS (tzfree, void, (timezone_t __tz));
+_GL_CXXALIAS_SYS (tzfree, void, (timezone_t __tz));
+_GL_FUNCDECL_SYS (localtime_rz, struct tm *,
+                  (timezone_t __tz, time_t const *restrict __timer,
+                   struct tm *restrict __result) _GL_ARG_NONNULL ((2, 3)));
+_GL_CXXALIAS_SYS (localtime_rz, struct tm *,
+                  (timezone_t __tz, time_t const *restrict __timer,
+                   struct tm *restrict __result));
+_GL_FUNCDECL_SYS (mktime_z, time_t,
+                  (timezone_t __tz, struct tm *restrict __result)
+                  _GL_ARG_NONNULL ((2)));
+_GL_CXXALIAS_SYS (mktime_z, time_t,
+                  (timezone_t __tz, struct tm *restrict __result));
+# endif
+
 /* Convert TM to a time_t value, assuming UTC.  */
 # if @GNULIB_TIMEGM@
 #  if @REPLACE_TIMEGM@
diff --git a/lib/time_rz.c b/lib/time_rz.c
new file mode 100644
index 0000000000..8a4d7d13a2
--- /dev/null
+++ b/lib/time_rz.c
@@ -0,0 +1,374 @@
+/* Time zone functions such as tzalloc and localtime_rz
+
+   Copyright 2015 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program; if not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+/* Although this module is not thread-safe, any races should be fairly
+   rare and reasonably benign.  For complete thread-safety, use a C
+   library with a working timezone_t type, so that this module is not
+   needed.  */
+
+#include <config.h>
+
+#include <time.h>
+
+#include <errno.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if !HAVE_TZSET
+static void tzset (void) { }
+#endif
+
+/* A time zone rule.  */
+struct tm_zone
+{
+  /* More abbreviations, should they be needed.  Their TZ_IS_SET
+     members are zero.  */
+  timezone_t next;
+
+  /* If nonzero, the rule represents the TZ environment variable set
+     to the first "abbreviation" (this may be the empty string).
+     Otherwise, it represents an unset TZ.  */
+  char tz_is_set;
+
+  /* A sequence of null-terminated strings packed next to each other.
+     The strings are followed by an extra null byte.  If TZ_IS_SET,
+     there must be at least one string and the first string (which is
+     actually a TZ environment value value) may be empty.  Otherwise
+     all strings must be nonempty.
+
+     Abbreviations are stored here because otherwise the values of
+     tm_zone and/or tzname would be dead after changing TZ and calling
+     tzset.  Abbreviations never move once allocated, and are live
+     until tzfree is called.  */
+  char abbrs[FLEXIBLE_ARRAY_MEMBER];
+};
+
+/* The approximate size to use for small allocation requests.  This is
+   the largest "small" request for the GNU C library malloc.  */
+enum { DEFAULT_MXFAST = 64 * sizeof (size_t) / 4 };
+
+/* Minimum size of the ABBRS member of struct abbr.  ABBRS is larger
+   only in the unlikely case where an abbreviation longer than this is
+   used.  */
+enum { ABBR_SIZE_MIN = DEFAULT_MXFAST - offsetof (struct tm_zone, abbrs) };
+
+static char const TZ[] = "TZ";
+
+/* Magic cookie timezone_t value, for local time.  It differs from
+   NULL and from all other timezone_t values.  Only the address
+   matters; the pointer is never dereferenced.  */
+static timezone_t const local_tz = (timezone_t) 1;
+
+#if HAVE_TM_ZONE || HAVE_TZNAME
+
+/* Return true if the values A and B differ according to the rules for
+   tm_isdst: A and B differ if one is zero and the other positive.  */
+static bool
+isdst_differ (int a, int b)
+{
+  return !a != !b && 0 <= a && 0 <= b;
+}
+
+/* Return true if A and B are equal.  */
+static int
+equal_tm (const struct tm *a, const struct tm *b)
+{
+  return ! ((a->tm_sec ^ b->tm_sec)
+            | (a->tm_min ^ b->tm_min)
+            | (a->tm_hour ^ b->tm_hour)
+            | (a->tm_mday ^ b->tm_mday)
+            | (a->tm_mon ^ b->tm_mon)
+            | (a->tm_year ^ b->tm_year)
+            | isdst_differ (a->tm_isdst, b->tm_isdst));
+}
+
+#endif
+
+/* Copy to ABBRS the abbreviation at ABBR with size ABBR_SIZE (this
+   includes its trailing null byte).  Append an extra null byte to
+   mark the end of ABBRS.  */
+static void
+extend_abbrs (char *abbrs, char const *abbr, size_t abbr_size)
+{
+  memcpy (abbrs, abbr, abbr_size);
+  abbrs[abbr_size] = '\0';
+}
+
+/* Return a newly allocated time zone for NAME, or NULL on failure.
+   As a special case, return a nonzero constant for wall clock time, a
+   constant that survives freeing.  */
+timezone_t
+tzalloc (char const *name)
+{
+  size_t name_size = name ? strlen (name) + 1 : 0;
+  size_t abbr_size = name_size < ABBR_SIZE_MIN ? ABBR_SIZE_MIN : name_size + 1;
+  timezone_t tz = malloc (offsetof (struct tm_zone, abbrs) + abbr_size);
+  if (tz)
+    {
+      tz->next = NULL;
+      tz->tz_is_set = !!name;
+      extend_abbrs (tz->abbrs, name, name_size);
+    }
+  return tz;
+}
+
+#if HAVE_TZNAME
+/* If TZNAME_ADDRESS is nonnull, an assignment of a saved abbreviation.
+   TZNAME_ADDRESS should be either null, or &tzname[0], or &tzname[1].
+   *TZNAME_ADDRESS = TZNAME_VALUE should be done after revert_tz
+   (indirectly) calls tzset, so that revert_tz can overwrite tzset's
+   assignment to tzname.  Also, it should be done at the start of
+   the next localtime_tz or mktime_z, to undo the overwrite.  */
+static char **tzname_address;
+static char *tzname_value;
+#endif
+
+/* Save into TZ any nontrivial time zone abbreviation used by TM,
+   and update *TM (or prepare to update tzname) if they use the abbreviation.
+   Return true if successful, false (setting errno) otherwise.  */
+static bool
+save_abbr (timezone_t tz, struct tm *tm)
+{
+#if HAVE_TM_ZONE || HAVE_TZNAME
+  char const *zone = NULL;
+  char **tzname_zone = NULL;
+  char *zone_copy = (char *) "";
+# if HAVE_TM_ZONE
+  zone = tm->tm_zone;
+# endif
+# if HAVE_TZNAME
+  if (! (zone && *zone) && 0 <= tm->tm_isdst)
+    zone = *(tzname_zone = &tzname[0 < tm->tm_isdst]);
+# endif
+
+  /* No need to replace null zones, or zones within the struct tm.  */
+  if (!zone || ((char *) tm <= zone && zone < (char *) (tm + 1)))
+    return true;
+
+  if (*zone)
+    {
+      zone_copy = tz->abbrs;
+
+      while (strcmp (zone_copy, zone) != 0)
+        {
+          if (! (*zone_copy || (zone_copy == tz->abbrs && tz->tz_is_set)))
+            {
+              size_t zone_size = strlen (zone) + 1;
+              if (zone_size < tz->abbrs + ABBR_SIZE_MIN - zone_copy)
+                extend_abbrs (zone_copy, zone, zone_size);
+              else
+                {
+                  tz = tz->next = tzalloc (zone);
+                  if (!tz)
+                    return false;
+                  tz->tz_is_set = 0;
+                  zone_copy = tz->abbrs;
+                }
+              break;
+            }
+
+          zone_copy += strlen (zone_copy) + 1;
+          if (!*zone_copy && tz->next)
+            {
+              tz = tz->next;
+              zone_copy = tz->abbrs;
+            }
+        }
+    }
+
+  /* Replace the zone name so that its lifetime matches that of TZ.  */
+# if HAVE_TM_ZONE
+  if (!tzname_zone)
+    tm->tm_zone = zone_copy;
+# endif
+# if HAVE_TZNAME
+  tzname_address = tzname_zone;
+  tzname_value = zone_copy;
+# endif
+#endif
+  return true;
+}
+
+/* Free a time zone.  */
+void
+tzfree (timezone_t tz)
+{
+  if (tz != local_tz)
+    while (tz)
+      {
+        timezone_t next = tz->next;
+        free (tz);
+        tz = next;
+      }
+}
+
+/* Get and set the TZ environment variable.  These functions can be
+   overridden by programs like Emacs that manage their own environment.  */
+
+#ifndef getenv_TZ
+static char *
+getenv_TZ (void)
+{
+  return getenv (TZ);
+}
+#endif
+
+#ifndef setenv_TZ
+static int
+setenv_TZ (char const *tz)
+{
+  return tz ? setenv (TZ, tz, 1) : unsetenv (TZ);
+}
+#endif
+
+/* Change the environment to match the specified timezone_t value.
+   Return true if successful, false (setting errno) otherwise.  */
+static bool
+change_env (timezone_t tz)
+{
+  if (setenv_TZ (tz->tz_is_set ? tz->abbrs : NULL) != 0)
+    return false;
+  tzset ();
+  return true;
+}
+
+/* Temporarily set the time zone to TZ, which must not be null.
+   Return LOCAL_TZ if the time zone setting is already correct.
+   Otherwise return a newly allocated time zone representing the old
+   setting, or NULL (setting errno) on failure.  */
+static timezone_t
+set_tz (timezone_t tz)
+{
+  char *env_tz = getenv_TZ ();
+  if (env_tz
+      ? tz->tz_is_set && strcmp (tz->abbrs, env_tz) == 0
+      : !tz->tz_is_set)
+    return local_tz;
+  else
+    {
+      timezone_t old_tz = tzalloc (env_tz);
+      if (!old_tz)
+        return old_tz;
+      if (! change_env (tz))
+        {
+          int saved_errno = errno;
+          tzfree (old_tz);
+          errno = saved_errno;
+          return NULL;
+        }
+      return old_tz;
+    }
+}
+
+/* Restore an old setting returned by set_tz.  It must not be null.
+   Return true (preserving errno) if successful, false (setting errno)
+   otherwise.  */
+static bool
+revert_tz (timezone_t tz)
+{
+  if (tz == local_tz)
+    return true;
+  else
+    {
+      int saved_errno = errno;
+      bool ok = change_env (tz);
+      if (!ok)
+        saved_errno = errno;
+#if HAVE_TZNAME
+      if (!ok)
+        tzname_address = NULL;
+      if (tzname_address)
+        {
+          char *old_value = *tzname_address;
+          *tzname_address = tzname_value;
+          tzname_value = old_value;
+        }
+#endif
+      tzfree (tz);
+      errno = saved_errno;
+      return ok;
+    }
+}
+
+/* Restore an old tzname setting that was temporarily munged by revert_tz.  */
+static void
+restore_tzname (void)
+{
+#if HAVE_TZNAME
+  if (tzname_address)
+    {
+      *tzname_address = tzname_value;
+      tzname_address = NULL;
+    }
+#endif
+}
+
+/* Use time zone TZ to compute localtime_r (T, TM).  */
+struct tm *
+localtime_rz (timezone_t tz, time_t const *t, struct tm *tm)
+{
+  restore_tzname ();
+
+  if (!tz)
+    return gmtime_r (t, tm);
+  else
+    {
+      timezone_t old_tz = set_tz (tz);
+      if (old_tz)
+        {
+          tm = localtime_r (t, tm);
+          if (tm && !save_abbr (tz, tm))
+            tm = NULL;
+          if (revert_tz (old_tz))
+            return tm;
+        }
+      return NULL;
+    }
+}
+
+/* Use time zone TZ to compute mktime (TM).  */
+time_t
+mktime_z (timezone_t tz, struct tm *tm)
+{
+  restore_tzname ();
+
+  if (!tz)
+    return timegm (tm);
+  else
+    {
+      timezone_t old_tz = set_tz (tz);
+      if (old_tz)
+        {
+          time_t t = mktime (tm);
+#if HAVE_TM_ZONE || HAVE_TZNAME
+          time_t badtime = -1;
+          struct tm tm_1;
+          if ((t != badtime
+               || (localtime_r (&t, &tm_1) && equal_tm (tm, &tm_1)))
+              && !save_abbr (tz, tm))
+            t = badtime;
+#endif
+          if (revert_tz (old_tz))
+            return t;
+        }
+      return -1;
+    }
+}
diff --git a/lib/timegm.c b/lib/timegm.c
new file mode 100644
index 0000000000..11c485ff05
--- /dev/null
+++ b/lib/timegm.c
@@ -0,0 +1,38 @@
+/* Convert UTC calendar time to simple time.  Like mktime but assumes UTC.
+
+   Copyright (C) 1994, 1997, 2003-2004, 2006-2007, 2009-2015 Free Software
+   Foundation, Inc.  This file is part of the GNU C Library.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef _LIBC
+# include <config.h>
+#endif
+
+#include <time.h>
+
+#ifndef _LIBC
+# undef __gmtime_r
+# define __gmtime_r gmtime_r
+# define __mktime_internal mktime_internal
+# include "mktime-internal.h"
+#endif
+
+time_t
+timegm (struct tm *tmp)
+{
+  static time_t gmtime_offset;
+  tmp->tm_isdst = 0;
+  return __mktime_internal (tmp, __gmtime_r, &gmtime_offset);
+}